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We performed an extensive analysis of C-band SAR datasets provided by the European Space Agency (ESA) satellites ERS-1/2, Envisat ASAR, and Sentinel-1 in the period 1992–2020 aiming at reconstructing the multi-decadal spatial and temporal evolution of the surface displacements at the Brienz/Brinzauls landslide complex, located in canton Graubünden (Switzerland). To this end, we analyzed about 1000 SAR images by applying differential interferometry (InSAR), multitemporal stacking, and persistent scatterer interferometry (PSI) approaches. Moreover, we jointly considered digital image correlation (DIC) on high-resolution multi-temporal digital terrain models (DTM) generated from airborne surveys and InSAR results to compute 3-D surface deformation fields. The extensive network of GNSS stations across the Brienz landslide complex allowed us to extensively validate the deformation results obtained in our remote sensing analyses. Here, we illustrate the limitations occurring when relying on InSAR and/or PSI measurements for the analysis and interpretation of complex landslide scenarios, especially in cases of relevant spatial and temporal heterogeneities of the deformation field. The joint use of InSAR and DIC can deliver a better picture of the evolution of the deformation field, however, not for all displacement components. Since InSAR, PSI and DIC measurements are nowadays routinely used in the framework of local investigations, as well as in regional, national, and/or continental monitoring programs, our results are of major importance for users aiming at a comprehensive understanding of these datasets in landslide scenarios. [ABSTRACT FROM AUTHOR]

The Western European Alps display measurable surface deformation rates from leveling and GNSS data. Based on the time‐series analysis of 4 years of Sentinel‐1 data, we propose for the first time an InSAR‐based mapping of the uplift pattern affecting the Western Alps on a ∼350 × 175‐km‐wide area. This approach provides a denser spatial distribution of vertical motion despite the high noise level inherent to mountainous areas and the low expected deformation signal. Our results show consistency with other geodetic measurements at the regional scale, and reveal smaller‐scale spatial variations in the uplift pattern. Higher uplift rates are found within the external crystalline massifs compared to surrounding areas, in agreement with the variations expected from recent deglaciation and long‐term exhumation data. This work brings the first InSAR‐based geodetic clue of differential uplift within the Alpine belt in response to the surface and deep processes affecting the belt. Plain Language Summary: The surface of the Earth is constantly moving from about a few millimeters to a few centimeters per year in response to geological processes such as tectonic plate motions and gravitational re‐equilibrium. In the Western European Alps, where the mountain‐building phase of the belt is over, the processes at the origin of surface motions are under debate. Mapping surface displacements at the highest possible resolution is mandatory to better understand the evolution of the Alpine belt. Among other techniques, radar satellites can provide measurements of such displacements. Here, radar images from the recent Sentinel‐1 satellite allow us to improve the spatial resolution of vertical surface displacements in the Western Alps compared to previous techniques. Thanks to the unmatched frequency of acquisitions from this satellite, we are able for the first time in our study area to measure small‐scale spatial variations within the vertical motions. These variations appear correlated to distinct geological units. This brings new insights into the geological processes acting nowadays on the Western Alps. Key Points: We use four years of Sentinel‐1 radar acquisitions to derive interseismic line‐of‐sight velocities over the Western European AlpsInSAR‐derived velocities are consistent with other geodetic studies and provide increased spatial resolution of surface velocity patternsShort‐wavelength spatial variations show locally higher velocities localized on crystalline massifs, interpreted as higher uplift rates [ABSTRACT FROM AUTHOR]